Parallel synthesis of polyethylene glycol supported biaryl benzimidazoles and imidazopyridines

The parallel synthesis of 25 biaryl 1H-benzimidazoles, 1H-imidazo[4,5-b]pyr idines and 1H-imidazo[4,5-c]pyridines on soluble polyethylene glycol suppor t is described. Polymer-esterified biaryl aldehydes were prepared in parall el fashion by coupling polymer-bound aryl halides with o-, m-, or p-formyl benzene boronic acid in a first step. Subsequently the aldehydes were treat ed with o-arylenediamines to form the title compounds. Nitrobenzene was use d as solvent and oxidant in this one-pot conversion. The polymer support re mained stable under the drastic conditions (180 degrees C, 3d) necessary fo r quantitative conversion as determined by MALDI-TOF-MS. The recovery of th e polymer-bound products was good to excellent, but cleavage of the ester b ond off the polymeric support (up to 33%) was observed as the main side rea ction. Transesterification with sodium methanolate and subsequent purificat ion by solid phase extraction with strongly acidic ion exchange resin and f lash chromatography yielded the desired methyl ester.